Some types of voltage-driven semiconductor elements require application of a negative voltage to a conduction control terminal, that is, the gate, when turned off. Patent Literature 1 discloses a configuration in which the emitter potential of a semiconductor switching element 4a is controlled by an amplifier 7 so as to apply voltage of positive and negative polarities across the emitter and the gate of the switching element 4a. Patent Literature 2 discloses a configuration in which a drive power supply voltage is divided by a series circuit of capacitors 21 and 22 and the divided potential is applied to the emitter of an IGBT 2 so as to likewise apply voltage of positive and negative polarities.